I measured all the places I could and created the following "blueprints:"
The side panels were a little difficult to identify exactly where some points start and end as the front and bottom corners are significanlty rounded, about 1/2" from the start of the rount to the corner. All the measurements for rivet holes are to the center of the hole.
One thing I found out as I pulled it apart was that there is a bracket under the bottom panel that has two guides to hold the side panels in place. You can see them in the image below.
The back part of the side panel just slide to the outside edge. There is no guide on the back.
One other thing. I did some research on what kind of tartan fabric this is. The closest I could come was that this was a variation of Campbell Dress Tartan. Here are a couple images of the tartans I could find:
I think it is closest to the second sample. I couldn't tell how to purchase this fabric or how much it might cost. My plan now is to try and find an automotive upholsterer who might be willing to tackle a small job like this. They may have access to more unique fabrics like this.
Well that is it for now. Hope this helps anyone who is thinking of trying to make one of these.
Here are some more detailed pictures of the rivets and snaps along the top outer edge of the box and inside. These rivets seem to stiffen the top edge and fit into the cutouts along the side panels...
Here is the outside of the bag. The left side of the image is the BACK of the bag that opens up. Note the three rivets along the top. There is also a snap just above the last rivet to the right. I believe this is original to the bag and keeps the top from flopping all the way open and wrecking the rather fragile attachment to the main body of the bag.
Here is the inside view. The right hand side of the image is now the back of the bag. Notice the snap does NOT come all the way through... only the rivets. These rivets slot into the cutouts in the plywood side panels.
Close ups of the outside rivet and snap area AND the inside of a rivet. The are pretty unique rivets.
Hope this helps! If anyone needs additional photos or descriptions of these bikes, I'm happy to get the information to you.